1. Field of the Invention
The present invention relates to a rotation detector for a multi-rotation body which rotates for a finite number of revolutions of one revolution or more, and particularly, to a rotation detector suitable for detecting an absolute position of the multi-rotation body.
2. Description of the Related Art
Conventionally, there is proposed a rotation detector, as described in Japanese Examined Utility Model Publication No. 5-26487, using an increment-type encoder to detect a precise rotation angle within one revolution of a steering wheel. It also uses an absolute-type encoder to detect a rough rotation angle of more than one revolution of the steering wheel. The detector then combines the precise rotation angle and the rough angle to determine the rotation angle from a neutral position of the steering wheel
The increment-type encoder is composed mainly of a code plate that rotates integrally with a steering shaft and photointerrupters opposing each other via the code plate. This encoder can detect only rotation angles of the code plate within one revolution. However, since the code plate rotates integrally with the steering shaft, the detection accuracy is high.
The absolute-type encoder is composed mainly of a substrate on which a resistance pattern is formed, a reduced-speed rotating body having a brush that slidably contacts the resistance pattern, and a gear mechanism for transmitting rotation of the steering wheel to the reduced-speed rotating body. In this case, since the rotation of the steering wheel that rotates multiple times is reduced to rotation within one cycle of the reduced-speed rotating body via the gear mechanism, an absolute position of the steering wheel can be detected.
In installation of the rotation detector as described above in a steering unit of a motor vehicle, however, the reduced-speed rotating body of the absolute-type encoder must be set to a neutral state in the rotation direction. If the reduced-speed rotating body is erroneously installed in a state which deviates from the neutral point, a precise absolute position of the steering wheel cannot be detected.
For this reason, in the conventional example as described above, after the installation of the absolute-type encoder in the steering unit, resistances which vary depending upon the position where the resistance pattern and the brush slidably contact must be electrically measured. Then, according to the variation in the resistance, a rotation status of the reduced-speed rotating body must be checked. This causes a reduction in efficiency of the installation of the rotation detector.
Also, in the conventional example, the gear mechanism composed of a sun gear arranged on a rotor member, a ring-like gear arranged on a stator member, and a planet gear engaged between the sun gear and the ring-like gear is used as the absolute-type encoder. Therefore, the arrangement space of the gear mechanism occupies in the whole rotation detector is relatively large. This causes a problem in that miniaturization of the rotation detector is difficult.
Furthermore, since the planet gear always engages with both the sun gear and the ring-like gear, the reduced-speed rotating body supporting the planet gear is rotated even by a minute rotation of the steering wheel. Particularly, since the rotation (operation) rate is subsequently high in the vicinity of the neutral position, a problem is caused in that the resistance pattern is locally worn away.
An object of the present invention is, therefore, to provide a rotation detector having a simple structure, operating reliably, and having a capacity of checking quickly for erroneous installation as an encoder for detecting the rotation rate of a multi-rotation body that rotates for a finite number of revolutions of one revolution or more.
To achieve this object and other objects described herein, according to the present invention, a rotation detector for a multi-rotation body, as described below is provided.
The rotation detector for a multi-rotation body has a rotor member integrally rotating with a code plate of a rotary encoder, a rotary member arranged concentrically with the center of rotation of the rotor member, an intermediate gear for intermittently transmitting rotation of the rotor member to the rotary member, detecting elements for detecting an amount of rotation of the rotary member, and a stator member enclosing the rotary member, the intermediate gear, and the detecting elements.
In the rotation detector for a multi-rotation body the stator member has a detection window through which an indicator for indicating a neutral rotation position of the rotary member can be viewed.
In this arrangement, the intermediate gear may be supported by the stator member, and the indicator is arranged on the rotary member. Also, the intermediate gear may be supported by the rotary member, and the indicator may be arranged on at least one of the intermediate gear and the rotary member.
As described above, the intermediate gear may be supported either by the stator member or by the rotary member. In the case of the intermediate gear being supported by the stator member, however, the indicator must be arranged with the stator member. In the case of the intermediate gear being supported by the rotary member, the indicator may be arranged on at least one of the intermediate gear and the rotary member.
Furthermore, the detection window may be arranged on an outer peripheral wall of the stator member. Furthermore, the detection window may be arranged on a cover of the stator member.
In the present invention as described above, rotation of the rotor member is transmitted intermittently to the rotary member via the intermediate gear, and the amount of rotation of the rotary member is detected by means of the detecting elements such as photointerrupters. Concurrently, the detection window is arranged on the stator member that encloses the rotary member and the detecting elements to allow an indicator of the rotary member to be viewed.
According to the present invention configured as described above, a neutral rotation position of the rotary member can be visually checked, improving efficiency of installation of the rotation detector. Also, the intermediate gear intermittently transmits rotation of the rotor member to the rotary member. This provides an advantage in that the amount of local abrasion in structural components due to continuous operation can be significantly reduced.
Furthermore, the need for excessive large layout spaces for the individual structural components can be avoided. Therefore, miniaturization of the rotation detector for the multi-rotation body can be achieved.